In general, the present application relates to an image processing apparatus, an image processing method, an image processing program and an electronic apparatus. More particularly, the present application relates to an excellent image processing apparatus, an image processing method, an image processing program, and an electronic apparatus for extracting a characteristic point from typically an image obtained as a result of an image taking operation carried out on the user.
There is researched an input technology to the personal computer or the like to be applied to an input device for inputting a command issued by a user. The input technology is a technology for inputting a command indicated a gesture or a posture of the user.
In the input technology, in order to recognize a user command indicated by a gesture or a posture expressed by a hand of the user for example, it is necessary to accurately detect typically a shape created by a hand of the user or the position of the tip of a middle finger of the user from an image obtained as a result of an image taking operation carried out on the user.
There is a skin recognition system for detecting typically the shape of a hand of the user by detecting (or recognizing) a skin area representing a skin of a human being from an image obtained as a result of an image taking operation carried out on an image taking subject (refer to Suzuki Yasuhiro et al., Electrical Engineering Thesis C (Detection Method of Skin Region by Near-IR Spectrum Multi-Band), Japan, 2007, Vol. 127, No. 4).
In the above skin recognition system, an LED (light emitting diode) for radiating light with a wavelength λ1 to an image taking subject and an LED for radiating light with a wavelength λ2 different from the wavelength λ1 to the same image taking subject are driven alternately to emit the light to the image taking subject. A typical example of the light with the wavelength λ1 is the near infrared ray having a wavelength of 870 nm whereas a typical example of the light with the wavelength λ2 is the near infrared ray having a wavelength of 950 nm.
It is to be noted that the wavelength λ1 and the wavelength λ2 to be combined with the wavelength λ1 as described above are typically determined as follows. The wavelength λ1 and the wavelength λ2 are set at such values that the reflection ratio of the light with the wavelength λ1 radiated to the skin of a human being is higher than the reflection ratio of the light with the wavelength λ2 radiated to the skin of a human being whereas the reflection ratio of the light with the wavelength λ1 radiated to a subject other than the skin of a human being is about equal to the reflection ratio of the light with the wavelength λ2 radiated to the subject other than the skin of a human being.
Then, in the skin recognition system, the LED for radiating the light with the wavelength λ1 is used for creating a first photographing-result image while the light with the wavelength λ1 is being radiated to the image taking subject.
By the same token, the LED for radiating the light with the wavelength λ2 is used for creating a second photographing-result image while the light with the wavelength λ2 is being radiated to the image taking subject.
Then, on the basis of the first photographing-result image and the second photographing-result image, a skin area is detected from either the first photographing-result image or the second photographing-result image.
That is to say, the skin recognition system adopts a wavelength combination in which the wavelength λ1 and the wavelength λ2 are set at such values that the reflection ratio of the light with the wavelength λ1 radiated to the skin of a human being is higher than the reflection ratio of the light with the wavelength λ2 radiated to the skin of a human being as described above.
Thus, the luminance value of every pixel composing a skin area on the first photographing-result image is relatively large whereas the luminance value of every pixel composing a skin area on the second photographing-result image is relatively small. As a result, the absolute value of a difference in luminance value between every individual pixel included in the skin area on the first photographing-result image and the second photographing-result image is relatively large.
In addition, the skin recognition system adopts a wavelength combination in which the wavelength λ1 and the wavelength λ2 are set at such values that the reflection ratio of the light with the wavelength λ1 radiated to a subject other than the skin of a human being is about equal to the reflection ratio of the light with the wavelength λ2 radiated to the subject other than the skin of a human being as described above.
Thus, the luminance value of every individual pixel included in a subject existing on the first photographing-result image as a subject other than a skin area is about equal to the luminance value of a pixel included in the subject existing on the second photographing-result image to serve as a pixel corresponding to the individual pixel. As a result, the absolute value of a difference in luminance value between every individual pixel included in the subject other than the skin area on the first photographing-result image and the second photographing-result image is relatively small.
Accordingly, if the absolute value of a difference in luminance value between every individual pixel included in the skin area on the first photographing-result image taken by the skin recognition system and a pixel included in the skin area on the second photographing-result image taken by the skin recognition system to serve as a pixel corresponding to the individual pixel is relatively large, the skin recognition system is capable of determining that the areas on the first photographing-result image and on the second photographing-result image are skin areas.